The Diagenetic Role of Brittle Deformation in Compaction and Pressure Solution, Etjo Sandstone, Namibia: A Discussion

Russell J. Maharaj

doi:10.1086/629845

The Diagenetic Role of Brittle Deformation in Compaction and Pressure Solution, Etjo Sandstone, Namibia: A Reply

The Journal of Geology ◽

10.1086/629846 ◽

1996 ◽

Vol 104 (4) ◽

pp. 508-508

Author(s):

Warren W. Dickinson ◽

Kitty L. Milliken

Keyword(s):

Pressure Solution ◽

Brittle Deformation

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The Diagenetic Role of Brittle Deformation in Compaction and Pressure Solution, Etjo Sandstone, Namibia

The Journal of Geology ◽

10.1086/629751 ◽

1995 ◽

Vol 103 (3) ◽

pp. 339-347 ◽

Cited By ~ 27

Author(s):

Warren W. Dickinson ◽

Kitty L. Milliken

Keyword(s):

Pressure Solution ◽

Brittle Deformation

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Role of pressure solution in the formation of bedding-parallel calcite veins in an immature shale (Cretaceous, southern UK)

Geological Magazine ◽

10.1017/s0016756818000377 ◽

2018 ◽

Vol 156 (5) ◽

pp. 918-934 ◽

Cited By ~ 5

Author(s):

QINGFENG MENG ◽

JOHN HOOKER ◽

JOE CARTWRIGHT

Keyword(s):

Critical Role ◽

Maximum Principal Stress ◽

Feedback Mechanism ◽

Black Shales ◽

Pressure Solution ◽

Overburden Pressure ◽

Axis Orientation ◽

Calcite Veins ◽

Fibre Growth

AbstractBedding-parallel fibrous calcite veins in black shales (Cretaceous, southern UK) were investigated using a combined field, stable isotopic geochemistry, petrographic and crystallographic method to examine their formation mechanism. Calcite veins occur in all shale beds and are most abundant in the bituminous shales of the Chief Beef Beds. The calcite fibres in these veins exhibit either an antitaxial fibre growth with curvy stylolites as the median zone, or a predominantly syntaxial, upwards growth. The calcite veins range from –0.49 to 1.78‰ of δ13C values, and –6.53 to –0.03‰ of δ18O values, which are both similar to those of their host shales. Our petrographic observations demonstrate that subhorizontal and interconnecting microstylolite networks commonly occur within the calcite veins. Equant calcite grains in the median zones exhibit indenting, truncating and also interpenetrating grain contacts. It is interpreted that the fibrous calcite veins were sourced by neomorphic calcite from their host shales, with evidence from the δ13C signatures, pressure-solution features (stylolites, microstylolites and grain contact styles) and embedded fossil ghosts within the veins. The diagenetic fluids, from which calcite was precipitated, were a mixing of the original seawaters and 18O-depleted meteoric waters. Development of bedding-parallel calcite veins is considered to have been enhanced by pressure solution as a positive feedback mechanism, which was facilitated by the overburden pressure as the maximum principal stress. Calcite fibres, with a predominant subvertical c-axis orientation, exhibit a displacive growth in porous shales and a replacive growth at vein-limestone contacts. This study highlights the critical role of pressure solution in the formation of bedding-parallel calcite veins during burial and diagenesis of immature black shales.

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Brittle deformation effects on the geothermal area framework, in Southern Tuscany, by multiscale lineament domain analysis

10.5194/egusphere-egu21-10725 ◽

2021 ◽

Author(s):

Federico Rabuffi ◽

Massimo Musacchio ◽

Francesco Salvini ◽

Malvina Silvestri ◽

Maria Fabrizia Buongiorno

Keyword(s):

Remote Sensing ◽

Domain Analysis ◽

Multiscale Approach ◽

Geothermal Area ◽

Brittle Deformation ◽

Tectonic Structures ◽

Structural Framework ◽

Ophiolitic Rocks ◽

The Relationship

Remote Sensing is a proven tool to study the Earth's surface and allows to analyze the wide portion of the surfaces by using different platforms/sensors (e.g. optical and active remote sensing, lidar), giving the possibility of multidisciplinary and multiscale approaches. In the proposed study, remote sensing analysis provides the possibility to understand the relationship between tectonic structures, lithology, and geothermal manifestations, and to test these techniques to monitor geothermal areas. This study allowed us to better understand the structural framework of a geothermal area, located in Southern Tuscany, highlighting the role of brittle deformation to produce an enhanced pathway for fluid migrations and upwelling.The studied area is the &#8220;Parco Naturalistico delle Biancane&#8221; (PNB) in the Grosseto province and belongs to the Cenozoic Tyrrhenian-Apennine orogenic system. The tectonic framework includes a fault and thrust belt setting derived from the collision between the Corsica-Sardinia Block and Adriatic Plate during late Oligocene-Miocene times. This process determined the pile-up of several tectonic units which are, from the top: (1) Ligurian Units consisting of ophiolitic rocks and pelagic sediments (Jurassic - Oligocen); (2) Cretaceous-Oligocene terrigenous deposits; (3) The Mesozoic Tuscan Nappe. Successively, the belt was affected by a regional, mainly extensional tectonics, then a magmatic intrusion affected this thinned Tyrrhenian belt to form the Tuscan Magmatic Province. In Recent time, the region underwent a general, yet differentiated uplift, and the major geothermal areas locate to the relative higher zone. This provides the Southern Tuscany to be the main Italian geothermal area.In this study, we analyzed the area from several points of view. The lineament domain analysis was performed in a multiscale approach: from 90 meters to 5 meters of pixel size, including 30 m and 10 m. This multiscale analysis allowed the identification of a number of lineament clusters related to the different tectonic phases which affected the PNB area. The found lineament distribution (in terms of azimuth and length) reflects the geodynamics effects on the surface, their clustering was related to the various crustal stress trajectories both at the regional and local scales.

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